Radio frequency communication receivers that support antenna diversity for overcoming some symptoms of multipath fading in a mobile environment are well known in the art. Examples of such receivers may be found in cellular mobile telephone systems. Other examples of such receivers may be found in systems such as those based on second generation digital cordless telephony (CT2) technology.
Some conventional radio communication receivers that support antenna diversity make the decision about which antenna should be used for receiving the incoming signal based upon received signal strength criteria. For example, whenever the received signal strength of the incoming signal falls below a predetermined level, the receiver switches to a different antenna in order to attempt to get better reception. Conventional CT2 digital communication transceivers that support antenna diversity make decisions about which antenna to use based upon either received signal strength or detected checksum errors.
Unfortunately, there are drawbacks to using received signal strength as a trigger for switching antennas. The drawback results from the effects of delay dispersion caused by selective multipath reflections of signals, and from interference signals. Both delay dispersion and interference signals can comprise substantial amounts of received signal strength, thus "fooling" antenna diversity trigger mechanisms based on received signal strength. This can cause a diversity system to remain coupled to a current antenna selection, when switching to an alternate antenna would likely produce better results.
Using detected checksum errors as a trigger for switching antennas can overcome the aforementioned drawback associated with received signal strength, but introduces a new problem. The new problem results from the amount of time it can take to detect an error. For example, during user communications in the CT2 system, a forty to eighty millisecond period is required to detect a checksum error in a relatively slow signaling data stream that accompanies the user communications. The possible loss of user communications for a corresponding forty to eighty milliseconds before switching to a better antenna can be very objectionable to system users.
Thus, what is needed is a way of controlling antenna diversity that performs well even in the presence of delay dispersion and interference, and that performs quickly enough to switch antennas before a degrading signal can cause an objectionable loss of user communications.